Leak detecting device

ABSTRACT

A leak detecting device of the counterflow type includes a high vacuum pump having an inlet connected to a mass spectrometer. In addition, a prevacuum pump is provided having an inlet connected to an outlet of the high vacuum pump and a leak detecting device input. A connecting conduit is further provided between the leak detecting device input and an intermediate inlet of the high vacuum pump. A first valve of variable conductance is arranged in the course of the connecting conduit. Valves with a large inner diameter are expensive while valves with a small inner diameter show considerable resistance even in a fully opened state. A second valve arranged parallel to the first adjustable valve is provided in the course of the connecting conduit; thereby allowing the first and second valves to have relatively small inner diameters arranged in the connecting conduit, wherein the combined conductance of both opened valves is considerably increased.

FIELD OF THE INVENTION

The invention relates to a leak detecting device working according tothe counterflow type.

BACKGROUND OF THE INVENTION

Such a leak detecting device is known from WO 96/24828. In a leakdetecting device of this type, the sensitivity and the detection limitof the leak detecting device can be respectively adjusted. To this end,the high vacuum pump the inlet of which is connected with a massspectrometer and the outlet of which is connected with a prevacuum pumpis provided with an intermediate inlet which is connected to the leakdetecting device input via a connecting conduit. In the course of theconnecting conduit, a valve of adjustable conductance is provided. Theadjustable valve serves as an adjustable throttle while the pressure atthe leak detecting device input is so high that an unthrottledconnecting conduit in the mass spectrometer would lead to an internalpressure that is so high that the mass spectrometer does not work. Forreasons of costs, the inner diameter of the valve is limited to adiameter as small as possible. Thereby, however, a considerable throttleeffect is maintained, reducing the suction capacity, even if the valveis completely open.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an inexpensive leakdetecting device having an improved suction capacity.

This object is solved, according to the invention.

The leak detecting device according to the invention comprises a secondvalve in the course of the connecting conduit, which is arrangedparallel to the adjustable first valve. By the second valve, the overallconductance of all opened valves in the course of the connecting conduitis considerably increased so that a good overall conductance can also berealized with relatively inexpensive valves with a small inner diameter.Thus, the need of a very expensive single valve with a large innerdiameter, i.e., with a high conductance, can be avoided. Both valves arearranged parallel to each other, i.e., they are parallel to each otherin the course of the only connecting conduit between the leak detectingdevice input and the only intermediate inlet of the high vacuum pump.

With leak detecting devices with a dry-running pump, e.g., a diaphragmpump, as a prevacuum pump, a test chamber connected to the leakdetecting device input is initially evacuated down to about 10-5 mbar.As soon as the vacuum has reached or passed below this pressure range,the adjustable first valve is slowly opened. The regulation of theadjustable valve can be effected in dependence on the input pressure,i.e., in dependence on the pressure at the input of the leak detectingdevice. Since the adjustable first valve is not completely opened, ameasurement may already be started at prevacuum pressure values stillclearly above the maximum admissible pressure at the intermediate inputof the high vacuum pump because the adjustable first valve acts as athrottle. Because of the throttle effect, such a low pressure isgenerated at the intermediate inlet of the high vacuum pump that themaximum admissible pressure is not reached in the mass spectrometereither and the mass spectrometer may already start measuring. Theconductance of the adjustable valve in the connecting conduit is setsuch that it is as high as possible, the maximum admissible pressure inthe mass spectrometer, however, is not exceeded. As soon as theprevacuum pressure value falls below a predetermined limit, theadjustable valve can be fully opened and the second valve can be fullyopened as well. Thereby, the combined conductance of the two valves inthe connecting conduit is increased so that the suction capacity of thehigh vacuum pump can be fully utilized as well.

In oil-sealed prevacuum pumps, the leak detecting device input isevacuated to about 1 mbar, and when the pressure decreases below thisvalue, the adjustable first valve is opened first, and later on, thesecond valve in the course of the connecting conduit is opened. Thereby,a sensitive measurement is made possible at an early time. From apressure of 10⁻² mbar up, both parallel valves can be fully opened toprovide a suction capacity at the leak detecting device input, which isas great as possible.

By providing a second valve parallel to the first adjustable valve, ahigh conductance is obtained when the valves are open, whereby valveswith a relatively small diameter or cross-section may be used, which areavailable at low costs.

According to one version of the invention, the second valve is a switchvalve that can be switched between an open and a closed condition. Thesecond valve serves to increase the conductance of the overall valvearrangement. Thus, there is no need for an adjustable valve for thesecond valve and an inexpensive switch valve may be used.

Preferably, the adjustable first valve is continuously adjustable.Thereby, the first valve can be continuously adapted to the pressureconditions.

According to one version of the invention, the inner diameter of each ofthe first and the second valves is smaller than 13 mm. Valves with aninner diameter of less than 13 mm are relatively inexpensive so that theoverall valve arrangement in the connecting conduit can thus be realizedin a more inexpensive manner than in the form of a single valve with acorrespondingly large inner diameter.

Preferably, a regulation device with a modulation module is providedwhich controls the opening of the adjustable first valve and modulatesthe gas flow through the adjustable first valve. By modulating the gasflow through the connecting conduit into the intermediate inlet of thehigh-vacuum pump, the sensitivity can be increased since the effectivesignal can be filtered out of the total signal by modulation. Themodulation by the adjustable first valve can be effected with the secondvalve opened or closed.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, an embodiment of the invention is explained in detail withreference to the drawing.

FIG. 1 shows an embodiment of a leak detecting device of the counterflowtype, according to the invention.

DETAILED DESCRIPTION

In the FIGURE, a leak detecting device 10 is illustrated which comprisesa leak detecting device input 12 to which a test chamber 14 with a testsample 16 is connected. The test sample 16 contains a test gas, e.g.,helium, of which even small amounts are detected by the leak detectingdevice 10.

The leak detecting device 10 is substantially formed by a prevacuum pump20, a high vacuum pump 22 and a mass spectrometer 24 which areinterconnected by gas lines in this order. Further, a bypass line 26 isprovided between the leak detecting device input 12 and an inlet 21 ofthe prevacuum pump 20, and a connecting conduit 30 is provided betweenthe leak detecting device input 12 and an intermediate inlet 28 of thehigh vacuum pump 22. In the course of the connecting conduit 30, twovalves are arranged, namely a first valve 32 that is continuouslyadjustable with respect to its conductance and parallel thereto a secondvalve 34 that is configured as a switch valve. In the course of thebypass line 26, a bypass line stop valve 38 is provided and in theconduit 25 between the prevacuum pump inlet 21 and a high vacuum pumpoutlet 23, a high vacuum pump stop valve 40 is provided. For detectingthe pressure, a test chamber pressure measuring apparatus 42 is providedat the leak detecting device input 12 and a prevacuum pressure measuringapparatus 44 is provided at the outlet 23 of the high vacuum pump 22.For controlling and regulating the leak detecting device 10, aregulation device 46 is provided which, among other things, comprises amodulation module 48 and a valve control module 50. The high vacuum pump22 is a turbomolecular pump but may also be configured as a frictionvacuum pump of a different configuration.

The prevacuum pump 20 is configured as a dry-running pump, e.g., as adiaphragm pump, but may also be configured as an oil-sealed prevacuumpump.

The adjustable first valve 32 is a continuously controllableproportional valve with an inner diameter of 6 mm. The second valve 34is a switch valve that is adapted to be switched between a fully openand a fully closed state and also has an inner diameter of 6 mm.

The prevacuum pressure measuring apparatus 44 and the test chamberpressure measuring apparatus 42 are connected to the regulation device46 by respective signal lines.

The two stop valves 38, 40 as well as the two valves 32, 34 in thecourse of the connecting conduit 30 are connected to the regulationdevice 46 via respective control lines.

In order to detect a leak by means of the leak detecting device 10, thetest chamber 14 with a test sample 16 containing the test gas helium isconnected to the leak detecting device input 12. Both the high vacuumpump stop valve 40 and the two valves 32, 34 arranged in the connectingconduit 30 are initially closed while the stop valve 38 in the bypassline is open. The prevacuum pump 20 is switched on and evacuates thetest chamber 14 via the bypass line 26. As soon as the test chamberpressure measuring apparatus 42 detects a pressure below 5 mbar, thehigh vacuum pump stop valve 40 is opened so that test gas is able toflow in counterflow through the high vacuum pump 22 to the detector, themass spectrometer 24, and can be detected there. The bypass line stopvalve 38 is closed.

From a test chamber pressure of 5 mbar on downward, the first valve 32which is of variable conductance is slowly opened by the regulationdevice 46 and the valve control module 50. The first valve 32 isrespectively opened only to such a degree that the gas pressure at theintermediate inlet 28 of the high vacuum pump 22 is below a pressurevalue at which a sufficiently low pressure is secured in the massspectrometer 24. With the test chamber pressure further decreasing, thefirst valve 32 is opened farther so that the conductance of the firstvalve 32 increases. As soon as the test chamber pressure has reached themaximum admissible pressure at the intermediate inlet 28, the firstvalve 32 is completely opened and the second valve 34 is opened as well.By opening the second valve 34, the combined conductance of the valvearrangement consisting of the two valves 32, 34 of the connectingconduit 30 is significantly increased immediately so that the suctioncapacity of the high vacuum pump 22 is not degraded by the fully openedvalves 32, 34.

Regulating and opening the two valves 32, 34 in the connecting conduit30 is automatically effected by the regulation device 46 in dependenceon the test chamber pressure.

To increase the measuring sensitivity, the valve control module 50 canbe driven by the modulation module 48 in such a manner that theconductance of the first adjustable valve 32 is modulated at a constantfrequency, while the second valve 34 is either open or closed. Themeasuring signal generated by the mass spectrometer 24 iscorrespondingly filtered in the regulation device 46 so that only theeffective signal is available for being evaluated.

1. A leak detecting device of the counterflow type, said devicecomprising: a high vacuum pump having an inlet connected to a massspectrometer; a prevacuum pump having an inlet connected to an outlet ofthe high vacuum pump and a leak detecting device input; a connectingconduit between the leak detecting device input and an intermediateinlet of the high vacuum pump; a first valve in the course of theconnecting conduit, said first valve having an adjustable conductance;and a second valve in the course of the connecting conduit, said secondvalve being arranged parallel to the adjustable first valve.
 2. A leakdetecting device according to claim 1, wherein the second valve is aswitch valve that is adapted to be switched between a fully opened and afully closed state.
 3. A leak detecting device according to claim 1,wherein the conductance of the adjustable first valve is continuouslyadjustable.
 4. A leak detecting device according to claim 1, wherein theinner diameter of each of the first and second valves is smaller than 13mm.
 5. A leak detecting device according to claim 1, wherein theprevacuum pump is an oil-sealed pump.
 6. A leak detecting deviceaccording to claim 1, wherein the prevacuum pump is a dry-running pump.7. A leak detecting device according to claim 1, further comprising aregulation device having a modulation module that controls the openingof the adjustable first valve and modulates the gas flow through theadjustable first valve.